1. Field Of The Invention
This invention relates to method and apparatus for nonrotatably connecting a pair of telescopically assembled elongated members and more particularly to a method for slidably connecting telescoping members having a preselected degree of tolerance in the nonrotational connection of the telescopic members substantially free of backlash.
2. Description of the Prior Art
In steering devices of motor vehicles it is known to connect the steering wheel to the axle or steerable members of the vehicle by a shaft or steering tube assembly that includes a pair of tubular, concentrically positioned elongated members that are nonrotatably connected to one another. The members are movable longitudinally relative to each other to facilitate assembly and disassembly of the portion connected to the steering wheel to the portion connected to the axle. The elongated members include interfitting connecting end portions where one end portion fits within the other for the transmission of torque from the steering wheel portion to the portion connected to the axle or under carriage of the vehicle. With this arrangement, the interconnecting members are drivingly connected and slide longitudinally relative to each other for assembly and disassembly, as well as, to provide relative movement between the members in response to the forces tansmitted to the lower member by movement of the vehicle over the road surface, as when the vehicle is traveling on a rough or undulatory road surface.
To facilitate the longitudinally slidable, nonrotatable connection of the telescoping members, the contour of the exterior surface of the inner connecting member is complementary with the contour of the inner surface of the outer connecting member. The shape of the contour for facilitating the nonrotatable connection must exhibit a close tolerance fit to minimize backlash in the transmission of torque from one member to the other. The contour of the inner connecting members is selective, for example the shapes may be square, hexagonal, octagonal, three leaf clover design, four leaf clover design, etc. Regardless of the shape of the interconnecting end portions, the chosen contour includes surfaces that are engagable for transmission of torque.
U.S. Pat. No. 4,667,530 illustrates the cross-sectional configuration of the interconnecting end portions of a vehicle steering shaft that includes rounded corners where the shape of the outer shaft approximately matches the shape of the inner shaft. The inner dimensions of the outer member and the outer dimensions of the inner member are different so that considerable play exists between the two parts. The gap that is formed between the two parts is bridged by a sleeve fabricated of suitable plastic material having a low coefficient of friction. The peripheral contour of the sleeve matches the contour of the member on which it is carried. The sleeve has a wall thickness which is dimensioned such that it bridges the gap between the two members so as to reduce the play therebetween. While the sleeve fills the gap between the two members, the sleeve is not stressed in the radial direction and the interconnected members remain longitudinally movable relative to each other.
One of the difficulties encountered in fabricating interconnecting rotation transmission members that must also slip longitudinally relative to each other is machining the interconnecting end portions so as to provide a very close tolerance fit that allows only a minimum amount of backlash. While the interconnecting parts may be machined, each machined part is subject to deviation to a slight extent from the specifications due to variations in the thickness of the tube wall, roundness, lubrication of surfaces, and temperature resulting in differential expansion and contraction of the interfitting end portions. The machining operations that are utilized to take into account the various factors which affect the tolerance between the interconnecting members add substantially to the manufacturing expense of the telescoping assembly.
In order to avoid rotational slippage in the transmission of torque for the nonrotatable connection of telescoping members a number of solutions have been proposed to obtain the effects of a very close tolerance fit. British Patent No. 5163 discloses in a cycle frame the connection of a pair of tubular members in which the corrugated end of a tube is inserted into a socket end of another member having a corrugated configuration that mates with the corrugated configuration of the tube. To obtain a secure joint, the tube and socket are coated with tin in a liquid state at an elevated temperature. When cooled to ambient temperature, the metal hardens to adhesively connect the two members. However, the members are not longitudinally movable relative to each other.
British Patent No. 10180 discloses a similar arrangement in which a cylindrical member is inserted within a star-shaped member where the gap or clearance between the two interfitting members is taken up by a bushing having an inner surface conforming to the outer surface of the inner member and an outer star-shaped surface conforming with the inner contour of the outer member.
U.S. Pat. No. 4,807,351 discloses a method for nonrotatably connecting tubular members of a vehicle drive shaft. In this application, the tolerances between the interfitting members must be so close that there is no slippage upon the application of torque to the connected members. To assure that there is no rotational slippage between the interconnected members, the end portions are joined by a splined connection where the splines are smooth continuous undulating surfaces which are swaged together by an electromagnetic process. While this arrangement nonrotatably connects the interfitting members, the members are not slidable longitudinally relative to one another.
A splined connection between a compressor shaft and turbine shaft in a gas turbine engine is disclosed in U.S. Pat. No. 3,393,533. The turbine shaft is provided with roughly machined external splines that engage the roughly machined internal splines of the compressor shaft. An annular space is provided between the engaging spines and is filled with a thermosetting synthetic resin material. Upon curing, the resin material permits torque to be transmitted from one shaft to the other while the annular space between the splined connection is filled with the resin material. Upon curing of the resin material, the shafts are not movable longitudinally relative to one another. In order to disassemble the shafts, the resin filler material must be sheared.
U.S. Pat. No. 4,977,793 discloses for use in an automotive engine application, the nonrotatable connection of a star-shaped cam element to a cam shaft. The cam shaft has an external configuration complementary to the internal star-shaped configuration of the cam element. An annulus is provided between the opposing contoured surfaces. A flowable plastic material is injected into the annular space. Upon hardening, the plastic material shrinks to interlock the shaft to the cam elements. The resin is chosen to withstand the torque between the cam elements and shaft.
U.S. Pat. Nos. 2,508,832; 2,725,692; and 4,600,222 are further examples of devices for interconnecting telescopic members for a rotation transmission having very close tolerances at substantially reduced rotational slippage or backlash.
While it has been suggested by the prior art devices to nonrotatably connect telescoping members for rotation transmission, it is extremely difficult and expensive to obtain close tolerances in a metal to metal fit. Also in a metal to metal fit for steering tube assemblies, the forces applied by one member to the other member are transmitted to the steering wheel which presents to the driver a coarse or rough feel when the vehicle travels a rough road surface as opposed to a more desirable cushioned feel. As an alternative, roughly machined interconnecting parts are connected using a filler material such as a rubber sleeve or high temperature thermoplastic material. It is also known to utilize a nylon coating on an inner connecting member which may then be machined more economically than a metal to metal fit to engage the inner surface of the outer connecting member in a very close tolerance. However, this also requires machining tasks which add to the time and expense of manufacturing the telescoping members.
It is also known to use filler materials, such as rubber gaskets and thermoplastic material injected at high temperatures to fill the annular space formed between roughly machined interconnecting parts However, the filler materials while providing for a very close tolerance fit which prevent slippage in the transmission of torque do not permit the interconnected members to move longitudinally relative to one another without shearing the filler material from the members. Therefore, there is need in a telescoping arrangement of interconnecting members for apparatus that facilitates efficient assembly of the connecting members with a very close tolerance fit that minimizes backlash while permitting the members to slide longitudinally relative to one another for assembly and disassembly.